The proposed project deals with biological molecules containing metallic ions. The objectives are to investigate the structural features of localized regions in such molecules, in the immediate vicinity of the metallic ions. For this purpose we employ a method - now generally known as EXAFS (Extended X-ray Absorption-edge Fine Structure) - which is based on the characteristics of the X-ray absorption spectrum close to an absorption edge of the ion. Synchrotron radiation emitted by 2 - 3 GeV electrons circulating in a storage ring at the Stanford Linear Accelerator Center (SLAC) extends into the X-ray region and constitutes the radiation source for this work. Materials under investigation include certain metallo-porphyrins, metallo-proteins (including some enzymes) with emphasis on certain heme proteins.